Three phase electric power is a common method of transmitting electric energy. Typically, the three phases of the electric power source vary sinusoidally, have the same average voltage and frequency, and exhibit a fixed 120° (2π/3 radians) phase relationship with respect to each other. When applied to substantially resistive loads such as heaters, the phase currents exhibit minimal phase lead or lag with respect to applied voltage, realizing a power factor of 0.95 or greater. The peak voltage, peak current, and the voltage and current zero crossings for each of the phases therefore occur at equidistant, detectable intervals.
Generally, three phase power is applied to a three phase load in a manner where all of the phases are applied to the load at the same time via a switching method. As a result of this, during a switching event where all three phases are applied simultaneously to the load, at least one of the phases generates a rapid increase in current limited only by the inductance of the load circuit and electromagnetic interference (EMI) can be generated. Due to the non-linearity of the switching circuits, this EMI may be spread over a wide spectral range and may have strong energy components at higher order harmonics. Such EMI may interfere with other electronic systems, such as radio communications systems. Additionally, the switching event can generate heat in the switching circuits as the constituent switching devices switch between off and on states, especially if the switching occurs at a point in time when a particular phase of the power source will drive or is driving a high current. This loss can become particularly significant in burst mode or other applications in which power is applied and removed rapidly and continuously, such as in high precision temperature control systems.